In the last three years, about 250,000 of the 2 million fir trees on Mt Parnitha, Athens’s largest remaining green space, have died as the result of a complex process linked to reduced rainfall and worsened by increased pollution on the plain of Attica. If measures are not taken soon, Parnitha’s forest will be considerably depleted in the immediate future. «The problem began back in the 1960s,» said Giorgos Amorgianiotis, head of the mountain’s forestry service. «Dead trees were recorded as far back as 1930, but things got really out of hand in 1988-89 and 2000-2002. Similar phenomena have been observed in Vytina, Arcadia, on Mt Parnassus and elsewhere.» Panayiotis Tsopelas, a researcher at the Institute of Mediterranean Forest Ecosystems at the National Foundation for Agricultural Research (ETHIAGE), who has been monitoring the health of the fir trees, believes that the source of the destruction is not purely pathogenic. The simultaneous appearance of the phenomenon in areas that are far from each other rules out the likelihood of a pathogenic organism being responsible for the necrosis. A number of researchers in Greece and in other parts of Europe as well as in North America agree that the problem is directly related to periods of reduced rainfall. «The necrosis of fir trees over wide areas is usually observed when the annual average rainfall has been reduced over the previous year or two,» Tsopelas explained. Statistics confirm this view. In 1998 and 1999, when rainfall on Parnitha was at average levels, necrosis was only observed on 0.7 percent and 0.3 percent of the total tree population respectively. However, two years of drought followed and cases of necrosis increased to 3.5 percent in 2000 and 4.9 percent in 2001. In 2002, the percentage remained high, at 5.9 percent. Increased rainfall over the past two years has brought about a reduction – down to 0.9 percent this year – according to the latest data. «There is no doubt that necrosis in fir forests is directly related to periods of drought,» said Tsopelas. The problem is a complex one. «The trees that die during dry periods have been gradually weakened during previous years from the effects of various factors. Then, when they do not get enough water, they become vulnerable to insects that eat the bark, killing the tree,» he added. These trees are vulnerable as their defense mechanisms have been weakened. «An important factor in weakening trees is Viscum album, also known as mistletoe, which has attacked about 70 percent of fir trees on the upper slopes of Parnitha. There are other factors, such as insects and fungi, but to a lesser degree. Atmospheric pollution is also a major factor,» said Tsopelas. According to a 1997 study by agronomist Dimitris Velisariou for the Benaki Phytopharmacology Institute between June and September of that year, unacceptably high levels of tropospheric ozone were found on the mountain. «Tropospheric ozone is the major pollutant with negative effects on plants. We even found microscopic toxic symptoms on the fir needles, and these have been recorded in the international bibliography,» said Velisariou. «Personally, I believe that atmospheric pollution and ozone levels are among the main factors [in the weakening of fir trees] because each variety of fir, each ecosystem, has its own degree of sensitivity.» Further research has not been undertaken but Tsopelas said that a study is being made on the effects of acid rain on Parnitha’s fir forest.